This invention relates to a drill pipe component, and in particular to a component to be placed in a string of drill pipe to reduce the friction between the string and the hole wall.
In industries where long holes or bores are drilled, such as the oil and gas exploration and extraction industries, the friction which occurs due to contact between the drill string and the bore wall may result in a substantial increase in the torque required to rotate the string and the drill bit. Such contact also causes wear and damage to the steel casing used to line sections of the bore.
In an effort to avoid these difficulties there have been various proposals for friction reducing components to be mounted in or on the string. U.S. Pat. No. 5,261,498 (The Red Baron (Oil Tools Rental) Limited) describes a typical friction reducing component or sub, in which a bore wall contacting sleeve is mounted on the lower part of a mandrel via bearings and is axially retained on the lower mandrel part between a shoulder and an upper mandrel part. While this and other subs have been used successfully in numerous operations, the cost and complexity of such subs has limited their widespread adoption and use.
It is among the objects of embodiments of the present invention to provide a friction-reducing drill pipe component which is relatively simple in construction and is thus less expensive to manufacture and maintain.
According to the present invention there is provided a friction-reducing drill pipe component for forming part of a drill string, the component comprising a tubular mandrel having first and second ends for connection to adjacent components of the drill string, a sleeve mounted on the mandrel, and first and second stops on the mandrel for restraining the sleeve against axial movement relative to the mandrel, at least the first stop being removable from the mandrel to permit the sleeve to be removed over the first end of the mandrel.
In use, the major parts of the component may be disassembled simply by removing the first stop and then lifting the sleeve over the first end of the mandrel. This contrasts with conventional arrangements in which removal of the sleeve, if possible, requires, for example, the dismantling of the mandrel or heat treatment and expansion of the sleeve. Thus, maintenance and repair of components made in accordance with embodiments of the present invention is relatively simple and in many instances may be carried out on-site at a drilling location.
The sleeve may be rotatable relative to the mandrel or may be non-rotatable on the mandrel. In this area, components or subs in which the sleeve is fixed relative to a mandrel are described as xe2x80x9crotatingxe2x80x9d subs, as the sleeve rotates in the bore with the drill string. If the sleeve is rotatable on the mandrel such subs are described as xe2x80x9cnon-rotatingxe2x80x9d subs, as the sleeve remains stationary relative to the bore.
In non-rotating subs, bearings may be provided between the sleeve and mandrel, or the sleeve and mandrel may define bearing surfaces. Where bearings are provided these may be introduced into the gap between the sleeve and the mandrel through a port in the sleeve. Bearing lubricant may be trapped between the mandrel and sleeve, however it is preferred that the fluid in the bore provides the necessary lubrication, and to this end the spacing of the stops may be selected to provide a flow path between the stops and the sleeve ends. One of the upper stop and the upper end of the sleeve may be configured to permit flow of fluid therebetween in the event that the contact between the sleeve and bore wall causes the sleeve to be pushed upwardly into contact with the upper stop, for example the upper end of the sleeve or the stop may be scalloped. Alternatively, ports may be provided in the upper end of the sleeve.
Preferably, the first stop is in the form of a collar. The collar may engage with a screw thread formed on the mandrel or may be retained on the mandrel by releasable connectors. The releasable connectors may be in the form of bolts or pins or, most preferably, are in the form of sprung pins or dogs which normally extend radially from the mandrel to engage and retain the collar. The collar may define ports therethrough to allow the dogs to be pushed inwardly to allow removal of the collar. The collar may also define slots in communication with the ports so that the collar may be rotated to cover the pins. Where sprung dogs are utilised to retain the sleeve, the dogs may be pushed inwardly to permit removal of the sleeve. Thus, with this embodiment of the invention it is possible for unskilled personnel to remove and replace the sleeve using only very simple tools, such that components may be repaired on-site without requiring specialised assistance or equipment.
Preferably also, the second stop is in the form of a stop ring. The ring may be removable but is preferably integral with the mandrel. In the preferred embodiment the mandrel, the mandrel end connections and the second stop are machined from a single piece of metal. The first stop and the sleeve may each also be formed of single pieces of metal. Accordingly, the resulting connector has only a small number of parts and is therefore easily assembled and disassembled and may be of robust construction.
The sleeve may have a cylindrical outer surface, or may define axial or helical blades with slots therebetween, to facilitate passage of drilling fluid through the annulus between the drill string and the bore wall. The blades may be of resilient material, such as PTFE, PEEK polymeric material, or vulcanised neoprene, most preferably reinforced with metal or some other rigid structure. Alternatively, the blades may be of metal, such as steel or alloy. The metal blades may be integral with the sleeve or welded or otherwise bonded to the sleeve. The slots may be undercut.
According to another aspect of the present invention there is provided a friction-reducing drill pipe component for forming part of a drill string, the component comprising a tubular mandrel having first and second ends for connection to adjacent components of the drill string, and a sleeve mounted on the mandrel, the sleeve defining external blades with undercut channels therebetween.
According to a further aspect of the present invention there is provided a friction-reducing drill pipe component for forming part of a drill string, the component comprising a tubular mandrel having first and second ends for connection to adjacent components of the drill string, a sleeve mounted on the mandrel, and spring-mounted lock dogs mounted on the mandrel and operatively associated with the sleeve for releasably retaining the sleeve on the mandrel.